The same dry lubricant coating of self replenishing type and method of making

ABSTRACT

A DRY LUBRICANT COATING COMPRISING GRAPHITE FLUORIDE POWDER HAVING A LUBRICATING PROPERTY DISPERSED IN A COATING METAL IS ELECTROPHORETICALLY DEPOSITED ON A SUBSTRATE SIMULTANEOUSLY WITH THE ELECTROLYTIC DEPOSITION OF THE COATING METAL. THE GRAPHITE FLUORIDE IS PRODUCED BY REACTING CARBON OR GRAPHITE WITH FLUORINE AT A TEMPERATURE OF LOWER THAN 550*C.

US. Cl. 204-16 7 Claims ABSTRACT OF THE DISCLOSURE A dry lubricant coating comprising graphite fluoride powder having a lubricating property dispersed in a coating metal is electrophoretically deposited on a substrate simultaneously with the electrolytic deposition of the coating metal. The graphite fluoride is produced by reacting carbon or graphite with fluorine at a temperature of lower than 550 C.

- This invention relates to a dry lubricant coating of a self-replenishing type, method of application thereof to the surface of an article, such as a bearing, and a coated article so obtained.

The term self-replenishing type refers to the dry lubricant coating which replenishes itself its lubricating surface as it wears away during the use thereof, which will be described in detail hereinafter.

Heretofore when dry lubricants, waxes, and liquid lubricants are applied to a surface, it is known that the particles and liquids, instead of adhering tenaciously to the surface, are largely removed after the first use.

An object of this invention is to provide a coating composition and a coating technique which allows control of how much lubricant is on the surface at any moment.

Another object is to provide a novel coating composition which gives a lubrication coating which supplies lubrication as the substrate material Wears.

Another object is to provide a coated article of superior lubrication properties.

With respect to the graphite fluoride referred above, it was in 1934 that Ruff and Bretschneider first discovered that graphite or carbon and fluorine combined without combination at about 420 C. to form a grey-colored solid (Zeitschrift anorg. allgem. Chem). The approximate composition of this solid was (CF where x is nearly equal to 1. They called the compound carbon monofluoride. However, in this invention we call it graphite fluoride because there are many compounds consisting of carbon and fluorine, such as, carbon tetrafiuoride and fluorocarbon polymer, such as, polytetrafluoroethylene (Teflon of E. I. du Pont de Nemours & Co.).

A recent production of the inorganic high molecular weight graphite fluoride of this invention is disclosed in US. Pat. No. 3,397,087. In reference to the above formula (Clwe adopt (CF wherein the ratio of C to F is 1:1.

It has been found that graphite fluoride has several outstanding properties, one of which being a remarkable lubricating property. Recently, US. Pat. No. 3,607,747 was granted to the same assignees of this application in view of a discovery that the addition of graphite fluoride to a lubricating grease would improve the property of the grease considerably.

In accordance with this invention, the dry lubricant coating of the self-replenishing type wherein graphite flu- United States Patent ice oride particles are dispersed in a coating metal is deposited electrophoretically on a substrate simultaneously with the electrolytic deposition of the coating metal by the method which comprises subjecting the substrate to the process of codeposition in a coating bath consistin of a coating metal, graphite fluoride powder, and one or two additives having a good adsorptive activity for graphite fluoride, such as, watersoluble high molecular weight compounds, water-soluble organic solvents, and colloidal oxides.

Hitherto a process for the codeposition of a coating metal and insoluble inorganic salt particles added to a coating bath on a substrate has been proposed. However, this process relates to the method of coating a substrate with nickel by adding salt particles of such as, aluminum, magnesium, calcium, barium and strontium to an acid nickel plating bath to obtain a coated surface wherein salt particles are uniformly dispersed, and has its object to produce a corrosion resistant satin-like nickel coating on the substrate, but not to obtain the dry lubricant coating of the self-replenishing type of this invention. The codeposition of molybdenum disulfide prticles and a coating metal on a substrate has been also proposed to form a coated article. However, molybdenum disulfide is a hydrophilic compound so that the codeposition thereof with the metal can be presumed, but there arises a problem as to its resistant to chemicals and its lubricity.

In view of the outstanding lubricating property of graphite fluoride as a solid lubricant, we have established a novel process for the codeposition of a dry lubricant coating of a self-replenishing type and a metal on a substrate, though it is diflicult to make a good dispersion of graphite fluoride in water or oil.

Based on many experiments, we inventors have confirmed that the codeposition of graphite fluoride powder and metal can be effected by the use of a coating bath consisting of coating metal, graphite fluoride, and one or two additives having a good adsorptive activity for graphite fluoride selected from the group of water-soluble high molecular weight compounds, water-soluble organic solvents, and colloidal oxides, wherein graphite fluoride is well dispersed in the coating bath, and further, this codeposition can be repeated with good results.

It has been found, therefore, that when the sliding or friction surface of a machine element, such as, piston ring, piston pin, or bearing, codeposited with the dry lubricant coating of the self-replenishing type in accordance with this invention, this coated surface can be used with safety for an extended period of time owing to low friction and good lubrication. Thus, an effective technical improvement can be provided by this invention.

As described hereinbefore, graphite fluoride is produced by the reaction of carbon or graphite with fluorine, halogen fluoride or a mixture thereof with an inert gas at a temperature of less than 550 C. The configuration is as follows: fluorine is introduced between the layer lattice structure of the carbon or graphite and is chemically bonded with one remaining valence electron in the carbon atom in a covalent bond, and the molecular formula may be expressed as (CF),, and the molar ratio of carbon to fluorine is 1:1. The compound is a transparent white or grey solid powder.

Graphite fluoride does not soften, nor burn at a relatively high temperature, and is stable up to the temperature of 550 C. under atmospheric pressure. Besides, it has a specific gravity of 2.00 to 2.70, is resistant to corrosion by aggressive chemicals such as acids and alkalis, and has a high electric resistance. Graphite fluoride will neither be wet with water nor with oil, and its angle of contact with water is so that it has a strong repellence to oil as well as water, and besides, a lubricating property at an elevated temperature. Furthermore, graphite fluoride has the stability to chemicals even in such an acidic solution as a plating bath so that its property as a lubricant will never be deteriorated; and it is quite stable to a frictional heat produced at the boundary lubrication and an atmospheric condition.

We have discovered that graphite fluoride particles can be dispersed in water or a plating solution with one or two additives, such as, water-soluble high molecular weight compound, water-soluble organic solvent, and colloidal oxide.

In carrying out the process of this invention, three methods are preferred: (1) graphite fluoride particles are previously immersed in a water-soluble solvent, such as, alcohol, siloxane, dioxane, and ketone in order to substitute adsorptive gases on the surface thereof, and then the treated particles together with a slight amount of a water-soluble high molecular weight compound, such as, polyethylene glycol and polyvinyl alcohol are added into the plating bath; (2) graphite fluoride particles are adsorbed with a slight amount of colloidal oxide, such as, silicic acid anhydride and titania, and then the treated particles are added into the plating bath; and (3) graphite fluoride particles are adsorbed with a water-soluble high molecular weight compound only, and then the treated particles are added into the bath. Each of the above three methods proved to be effective to produce a dry lubricant coating film in which graphite fluoride particles are uniformly dispersed on a substrate of, preferably, the electric conductive property.

In this invention, the water-soluble organic solvent includes methyl alcohol, ethyl alcohol, propyl alcohol, glycol, glycerine, siloxane, acetone, and methyl ethyl ketone, etc. The water-soluble high molecular weight compound includes polyethylene glycol, polyvinyl alcohol, polyamine, polyvinyl carbazol, and polyacrylamide; and one, two or more of the above compounds can be employed.

In the application of this invention, when it is needed to make possible smoothing or levelling the coated surface, the addition of a brightener available in the market is desirable so that the use of the brightener in the plating bath does not affect the codeposition of this invention adversely, but can attain to produce a smooth coated surface.

In the codeposition of graphite fluoride particles dispersed in the coating metal on the substrate in accordance with this invention, it has been found that the larger the volume percentage of graphite fluoride dispersed in the coated film the less adhesion between the coated film and the substrate takes place. Accordingly, the upper limit of the volume percentage of graphite fluoride particles to be added to the coating solution in order to produce the dry lubricant coating of the self-replenishing type of this invention is preferred to be 80% by volume.

In particular, when the mechanical strength of the coated film, for example, deposited on the sliding surface of a machine element, such as, piston ring or bearing is required, the codeposition of a large amount of graphite fluoride particles should be obviated so that the amount thereof should be preferred to be less than 5%. In carrying out the process of this invention, the amount of graphite fluoride particles to be added to the plating bath should be less than 500 g. per liter, and the preferred concentration thereof should be in the range of 0.0001 to 50 g. per liter. Further, in the practical operation of the process, a mechanical agitation of the bath has proved to be beneficial.

To maintain a good adherence of the coated film to the substrate, it is required that the particle size of graphite fluoride should be divided as finely as possible, and less than microns. In particular, more than 80% of the particle size of graphite fluoride is preferred to be less than 0.5 micron.

The present invention will be described hereinbelow in connection with the preferred embodiments thereof. However, it is understood that this invention will not be limited by these examples, and various changes and modifications may be made depending upon the additive used, for example, the description and amount of organic solvent, and of Water-soluble high molecular weight organic compound. It is also understood that the coating or plating process in this invention will not be limited by electroplating only, but includes chemical as well as hot dip coating.

EXAMPLE 1 A solution was prepared wherein 0.3 g./l. of graphite fluoride particles having the mean particle size, 0.2 micron, in the spherical form were uniformly suspended in methyl or ethyl alcohol, and this uniform suspension is referred to A solution. Then, a nickel coating having the thickness of 25 microns was deposited on a brass sheet having the thickness of 2 mm. by the electrodeposition under the condition specified below in the plating bath of the following composition containing the above A solution:

For comparison, an additional test specimen was prepared from the coating bath which did not contain the above A solution at all, and then two tests for abrasion were conducted by means of Tabers Model 174 Abraser (Taber Instrument Corp., N.Y., USA.) on the above two test specimens in connection with the abrasion resistances, respectively, the test results of which are shown below:

Codcposited surface (this Coated surface invention) (prior art) Number of rotation (70 r.p.m.). 10 10 10x10 Amount of abrasion, mg 170.4 230.3 Taber abrasion, mg./1,0fl0 cycle... 1.70 2.30 Depth of abrasion trace, micron. 13 18 Surface hardness, HMV 599 648 It is clearly shown from the above that the nickel coated surface codeposited with a small amount of graphite fluoride in accordance with this invention has increased its lubricity as well as its abrasion resistance to a remarkable degree.

EXAMPLE 2 An aqueous dispersion of graphite fluoride was prepared by the steps of mixing one part of graphite fluoride particles, 0.25 part of colloidal anhydrous silicic acid, and two parts of polyethylene glycol No. 300 while these components were kneading under a reduced pressure for a period of one to two hours, and then adding the composition thus obtained to 50 parts of water while agitating. This aqueous dispersion is referred to B solution.

Then, a test specimen of a brass sheet 2 mm. thick coated with iron was prepared by the electrodeposition under the condition Specified below in the plating bath of the following composition containing the above B solution:

B solution cc./l 6 FeSO (NH )SO -6H O g./l 350 pH 3.0 Bath temperature C 25 Current density amp/dm. 2.5

For comparison, as in Example 1, an additional test specimen was prepared from the coating bath which excluded the above B solution under the same condition,

and then two tests for abrasion were conducted in connection with the coefficient of friction and the rate of abrasion, the results of which were shown below:

Codeposited surface (this Coated surface Description of friction invention) (prior art) Ratio of coefficient of friction 1 1.82 Rate of abrasion 1 2.11

From the above, it is seen that the lubricity and abrasion resistance of the surface codeposited with graphite fluoride and metal are considerably improved.

EXAMPLE 3 A suspension solution (referred to C solution) was prepared wherein 2 g. per liter of graphite fluoride powder were dispersed in dioxane. Then, a nickel coating layer, 15 micron thick, was deposited on a steel sheet by the electrodeposition under the condition specified below in the plating bath of the following composition containing the C solution:

C solution cc./l 20 Polyvinylalcohol g./l 6 Nickel pyrophosphate g./l 80 Potassium pyrophosphate g./l 300 Aqueous ammonium (specific gravity 0.88) cc./l pH 8.5 Current density amp/dm. 4 Bath temperature C 55 For comparison, as in Examples 1 and 2, an additional test specimen was prepared from the coating bath which excluded the C solution under the same condition, and then two tests for abrasion as in Example 2 were conducted, the results of which are shown below:

Codeposited surface (this Coated surface Description of test invention) (prior art) Ratio of coefficient of iriction 1 3.50 Rate of abrasion 1 4.20

We claim:

in a molar ratio of carbon to fluorine of 1:1, said graphite fluoride being obtained by reacting carbon or graphite with fluorine in an inert gas at a temperature lower than 550 C., and one or more dispersion promoting additives for the graphite fluoride selected from (1) a colloidal oxide selected from the group consisting of silicic acid anhydride and titania, (2) a Water-soluble organic solvent selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, glycol, glycerine, siloxane, acetone, and methyl ethyl ketone and (3) a watersoluble high molecular weight compound selected from the group consisting of a polyethylene glycol, a polyvinyl alcohol, a polamine, a polyvinyl carbazol and a polyacrylamide.

2. The improvement according to claim 1 wherein the dispersion promoting additive is selected from the group consisting of silicic acid anhydride and titania.

3. The improvement according to claim 1 wherein the dispersion promoting additive is selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, glycol, glycerine, siloxane, acetone and methyl ethyl ketone.

4. The improvement according to claim 1 wherein the dispersion promoting additive is selected from the group consisting of a polyethylene glycol, a polyvinyl alcohol, a polyamine, a polyvinyl carbazol and a polyacrylamide.

5. The improvement according to claim 1 wherein a brightener is used therein.

6. The improvement according to claim 1 wherein the concentration of graphite fluoride powder added thereto is in the range of 0.0001 g. to 500 g. per liter of said bath and the particle size of graphite fluoride is less than 10 microns.

7. The improvement according to claim 6 wherein more than of the graphite fluoride has a particle size of less than 0.5 micron.

References Cited UNITED STATES PATENTS 1,702,927 2/ 1929 Bezzenberger 204-181 2,999,798 9/ 1961 Esslingen 204-181 3,607,747 9/ 1971 Ishikawa 252-18 3 ,672,970 6/ 1972 Tomaszewski 204-181 FOREIGN PATENTS 728,043 2/ 1966 Canada 252-12 772,604 11/ 1967 Canada 252-12 THOMAS TUFARIELLO, Primary Examiner US. Cl. X.R. 

